Low gwp cascade refrigeration system

ABSTRACT

Disclosed are cascade refrigerant systems for providing cooling of air located in an enclosure that is occupied by or which will be exposed to humans or other animals during normal use, wherein systems includes; (1) a first, relatively low temperature heat transfer circuit having a first evaporator located within the enclosure and a first heat transfer fluid in the low temperature heat transfer circuit; (2) a second heat transfer circuit located substantially outside the enclosure comprising a second heat transfer fluid; (3) a heat exchanger which serves as the condenser in the low temperature circuit thermally coupled with the high temperature circuit by virtue of rejecting heat into the second heat transfer fluid; and (4) in the high temperature loop of a heat exchanger which transfers heat from the second heat transfer fluid exiting from a high temperature condenser to the portion of the second heat transfer fluid which is traveling to the suction side of the compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Provisional Application 62/313,177, filed Mar. 25, 2016, which is incorporated herein by reference in its entirety.

The present application is also a continuation-in-part of U.S. application Ser. No. 15/400,891, filed Jan. 6, 2017, now pending, which in turn claims the priority benefit of Provisional application 62/275,382, filed Jan. 6, 2016, each of which is incorporated herein by reference in its entirety.

The present application is also a continuation-in-part of U.S. application Ser. No. 15/434,400, filed Feb. 16, 2017, now pending, which in turn claims the priority benefit of 62/295,731, filed Feb. 16, 2016, the entire contents of each of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to high efficiency, low-global warming potential (“low GWP”) air conditioning and/or refrigeration systems and methods for providing cooling that are safe and effective.

BACKGROUND

In typical air conditioning and refrigerant systems, a compressor is used to compress a heat transfer vapor from a lower to a higher pressure, which in turn adds heat to the vapor. This added heat is typically rejected in a heat exchanger, commonly referred to as a condenser. The heat transfer vapor that enters the condenser is condensed to produce a liquid heat transfer fluid at a relatively high pressure. Typically the condenser uses a fluid available in large quantities in the ambient environment, such as ambient outside air, as the heat sink. Once it has been condensed, the high-pressure heat transfer fluid undergoes a substantially isoenthalpic expansion, such would occur by passing the fluid through an expansion device or valve, where it is expanded to a lower pressure, which in turn results in the fluid undergoing a decrease in temperature. The lower pressure, lower temperature heat transfer fluid from the expansion operation then is typically routed to an evaporator, where it absorbs heat and in so doing evaporates. This evaporation process in turn results in cooling of the fluid or body to that it is intended to cool. In many typical air conditioning and refrigeration applications, the cooled fluid is the air which is contained in the region to be cooled, such as the air in the dwelling being air conditioned or the air inside a walk-in cooler or a supermarket cooler or freezer. After the heat transfer fluid is evaporated at low pressure in the evaporator, it is returned to the compressor where the cycle begins once again.

A complex and interrelated combination of factors and requirements is associated with forming efficient, effective and safe air conditioning systems that are at the same time environmentally friendly, that is, have both low GWP impact and low ozone depletion (“ODP” impact. With respect to efficiency and effectiveness, it is important for the heat transfer fluid to operate in air conditioning and refrigeration systems with high levels of efficiency and high relative capacity. At the same time, since it is possible that the heat transfer fluid may escape over time into the atmosphere, it is important for the fluid to have low values for both GWP and ODP.

Applicants have come to appreciate that while certain fluids are able to achieve high levels of both efficiency and effectiveness, and at the same time low levels of both GWP and ODP, many fluids which satisfy this combination of requirements nevertheless suffer from the disadvantage of having deficiencies in connection with safety. For example, fluids which might otherwise be acceptable may be disfavored because of flammability properties and/or toxicity concerns. Applicants have come to appreciate that the use of fluids having such properties is especially undesirable in typical air conditioning and in many refrigeration systems since such flammable and/or toxic fluids may inadvertently be released into the dwelling, walk-in, cold-box, chiller, freezer or transport refrigeration box which is being cooled, thus exposing or potentially exposing the occupants thereof to dangerous conditions. Applicants have also come to appreciate that this problem is even of a more intense concern for relatively small systems, e.g., systems with a capacity of less than 30 kw since for such systems the cost of effective safety protection systems, such as fire protections systems, are frequently not economically viable.

SUMMARY

According to one aspect of the invention, a cascade refrigerant system is provided for providing cooling of air, directly or indirectly but preferably directly, located in an enclosure that is occupied by or which will be exposed to humans or other animals during normal use. As used herein, the term “enclosure” means a space that is at least partially confined (e.g., the enclosure can be opened on one or more sides, or closed) and includes air that has been cooled.

Preferred embodiments of the present systems include at least a first evaporator which is located within the enclosure and is part of a first, relatively low temperature heat transfer circuit. The low temperature heat transfer circuit preferably comprises a first heat transfer fluid in a vapor compression circulation loop comprising at least: a compressor for raising the pressure of the first heat transfer composition; a heat exchanger for condensing at least a portion of the first heat transfer composition from the compressor at a relatively high pressure; an expansion device for lowering the pressure of the heat transfer composition from the condenser; and an evaporator for absorbing heat from the enclosure to be cooled into the heat transfer composition. Preferably one or more of said compressor, condenser and said expansion valve, and most preferably all of these, are located outside the enclosure and the evaporator is located within the enclosure.

The systems of the present invention also preferably include a second heat transfer circuit located substantially outside the enclosure, which is sometimes referred to herein by way of convenience as the “high temperature” loop. The high temperature loop preferably comprises a second heat transfer fluid in a vapor compression circulation loop comprising at least a compressor, a heat exchanger which serves to condense the heat transfer fluid in the high temperature loop, preferably by heat exchange with ambient air outside of the enclosure, and an expansion device for reducing the pressure of the second heat transfer fluid from the compressor.

An important aspect of preferred embodiments of the present invention is that the heat exchanger which serves as the condenser in the low temperature circuit is thermally coupled with the high temperature circuit by virtue of rejecting heat into the second heat transfer fluid, preferably by causing at least a substantial portion of said second heat transfer fluid to evaporate. In this way, the condenser of the low temperature circuit and the evaporator of the high temperature circuit are thermally coupled in this heat exchanger, which is sometimes referred to for convenience as “a cascade heat exchanger” in the systems and methods of the present invention.

Another important aspect of the present invention in preferred embodiments comprises the presence in the high temperature loop of a heat exchanger which has been found to advantageously and unexpectedly improve system performance by transferring heat from the second heat transfer fluid exiting from the high temperature condenser to the portion of the second heat transfer fluid which is traveling to the suction side of the compressor. This heat exchanger is sometimes referred to herein for convenience as a “suction line heat exchanger.”

Another important aspect of the preferred systems is that the first heat transfer fluid which is circulating in the low temperature loop comprises a refrigerant which has a GWP of not greater than about 500, more preferably not greater than about 400, and even more preferably not greater than about 150 and furthermore that the first heat transfer fluid has a flammability that is substantially less than the flammability of the second heat transfer fluid. Preferably, the second heat transfer fluid which is circulating in the high temperature loop also comprises a refrigerant which has a GWP of not greater than about 500, more preferably not greater than about 400, and even more preferably not greater than about 150, but since in normal operation this heat transfer fluid will never enter the enclosure, applicants have found that is advantageous to use a fluid in this high temperature loop that has one or properties that would be considered disadvantageous if it circulated within the enclosure, for example, flammability, toxicity and the like. In this way, the present systems allow additional possible unexpected advantages over systems that would rely only of the first heat transfer composition or only the second heat transfer composition, as explained in detail below.

In certain preferred embodiments the second refrigerant comprises, more preferably comprises at least about 50% by weight and even more preferably at least about 75% by weight, of trans-1,3,3,3-trifluoropropene (HFO-1234ze(E) and/or HFO-1234yf, and the second refrigerant has a flammability greater than , and preferably substantially greater than about, the flammability of CO2. In another embodiment the second refrigerant comprises, more preferably comprises at least about 75% by weight and even more preferably at least about 80% by weight, of trans-1,3,3,3-trifluoropropene (HFO-1234ze(E) and/or HFO-1234yf.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized process flow diagram of one preferred embodiment of an air conditioning system according to the present invention.

FIG. 2 is a schematic of a typical walk-in cooler refrigeration configuration.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Preferred Heat Transfer Compositions

In each of the preferred embodiments described herein the system includes:

(a) a relatively low temperature vapor compression loop comprising a compressor, an expander and an evaporator in fluid communication in said loop, and a first heat transfer composition in said loop comprising a first refrigerant and preferably lubricant for the compressor, said evaporator being located in an enclosure containing air to be cooled and being capable of absorbing heat from said air at about said relatively low temperature;

(b) a relatively high temperature vapor compression loop comprising a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication in said loop, and a second heat transfer composition in said loop comprising a second refrigerant and preferably lubricant for the compressor, said condenser being capable of transferring heat to a heat sink located outside said enclosure; and

(c) a cascade heat exchanger for condensing said first refrigerant and evaporating said second refrigerant by heat exchange between said first and second refrigerant,

wherein said suction line heat exchanger is in fluid communication with said cascade heat exchanger for receiving at least a portion of said second heat transfer composition exiting said cascade heat exchanger and increases the temperature thereof by absorbing heat from said first heat transfer composition exiting said condenser and thereby reducing the temperature of said first heat transfer composition prior to said first heat transfer composition entering said first loop expander.

As used herein, the terms “relatively low temperature” and “relatively high temperature,” when used together with respect to the first and second heat transfer loops, and unless otherwise indicated, are used in a relative sense to designate the relative temperature of the indicated heat transfer compositions, where those differences are least about 5° C.

Preferably the first refrigerant has a flammability that is substantially less than the flammability of the second refrigerant. In preferred embodiments, the first refrigerant has a flammability according to ASHRAE Standard 34 (which specifies measurement according to ASTM E681) that is classified as Al and the second refrigerant has a flammability according to ASHRAE Standard 34 that is classified as A2L or a higher flammability than A2L, although A2L classification for the second refrigerant is preferred. It is also preferred that the first and the second refrigerant each have a Global Warming Potential (GWP) that is less than about 150.

In preferred embodiments the first refrigerant circulating in the low temperature loop comprises carbon dioxide, preferably consists essentially of carbon dioxide and more preferably in some embodiments consists of carbon dioxide.

It is preferred that the second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, and R-32 and combinations of two or more of these. In preferred embodiments, the second refrigerant comprises at least about 50%, more preferably at least about 80% by weight of 2, 3,3,3-tetrafluoropropene (HFO-1234yf). In other preferred embodiments, the second refrigerant comprises at least about 50%, more preferably at least about 80% by weight of or at least about 75% by weight, more preferably at least about 80% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)). In highly preferred embodiments, the second refrigerant comprises at least about 95% by weight, and in some embodiments consists essentially of or consists of HFO-1234ze(E), HFO-1234yf or combinations of two or more of these.

In other highly preferred embodiments, the second refrigerant comprises from about 70% by weight to about 90% of HFO-1234yf, preferably about 80% by weight of HFO-1234yf and from about 10% by weight to about 30% by weight of R32, preferably about 20% by weight of R-32.

In other highly preferred embodiments, the second refrigerant comprises from about 70% by weight to about 90% of HFO-1234ze(E), preferably about 80% by weight of HFO-1234ze(E) and from about 10% by weight to about 30% by weight of R32, preferably about 20% by weight of R-32.

In other highly preferred embodiments, the second refrigerant comprises from about 85% to about 90% by weight of by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight to about 15% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), and even more preferably in some embodiments about 88% of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and about 12% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).

Those skilled in the art will appreciate in view of the disclosures contained herein that the preferred embodiments of the present invention provide the advantage of utilizing only the safe (relatively low toxicity and low flammability) low GWP refrigerants within the enclosure to be cooled and a relatively less safe, but preferably low GWP refrigerant in the high temperature loop which is located entirely outside of the enclosure.

As used herein, the terms “safe” and “relatively less safe,” when used together with respect to the first and second heat transfer loops, and unless otherwise indicated, are used in a relative sense to designate the relative safety of the indicated heat transfer compositions. Such configuration, especially when the high temperature system includes the preferred suction line heat exchanger, makes the systems and methods of the invention highly preferred for use in a location proximate to the humans or other animals occupying or using the enclosure, as is commonly encountered in walk-in freezers, supermarket coolers and the like.

Preferred embodiments of the second refrigerant are disclosed in the following table:

Component>>> Second Refrigerant Designation R-1234yf, R-1234ze(E), ▾ ▾ wt % wt % R-32 R227ea SR1  5 95 0 0 SR2  10 90 0 0 SR3  15 85 0 0 SR4  20 80 0 0 SR4  25 75 0 0 SR5  30 70 0 0 SR6  35 65 0 0 SR7  40 95 0 0 SR8  45 50 0 0 SR9  50 50 0 0 SR10 55 45 0 0 SR11 60 40 0 0 SR12 65 35 0 0 SR13 70 30 0 0 SR14 75 25 0 0 SR15 80 20 0 0 SR16 85 15 0 0 SR17 90 10 0 0 SR18 95 5 0 0 SR19 70 0 30 0 SR20 75 0 25 0 SR21 80 0 20 0 SR22 85 0 15 0 SR23 90 0 10 0 SR24 0 70 30 0 SR25 0 75 25 0 SR26 0 80 20 0 SR27 0 85 15 0 SR28 0 90 10 0 SR29 0 80 0 20 SR30 0 85 0 15 SR31 0 88 0 12 SR32 0 90 0 10 SR33 0 95 0 5

The first heat transfer composition and the second heat transfer compositions also each generally include a lubricant, generally in amounts of from about 30 to about 50 percent by weight of the heat transfer composition, with the balance comprising refrigerant and other optional components that may be present. Combinations of surfactants and solubilizing agents may also be added to the present compositions to aid oil solubility, as disclosed by U.S. Pat. No. 6,516,837, the disclosure of which is incorporated by reference. Commonly used refrigeration lubricants such as Polyol Esters (POEs) and Poly Alkylene Glycols (PAGs), silicone oil, mineral oil, alkyl benzenes (ABs) and poly(alpha-olefin) (PAO) that are used in refrigeration machinery with hydrofluorocarbon (HFC) refrigerants may be used with the refrigerant compositions of the present invention. The preferred lubricants are POEs.

Preferred combinations of first refrigerant, second refrigerant and lubricant according to one aspect of the invention are provided below.

SECOND HEAT TRANSFER FIRST HEAT TRANSFER COMPOSITION COMPOSITION Regrig., Lub, Regrig., Lub, EMBODIMENT Refrig. wt % Lub wt % Refrig. wt % Lub wt % 1 1234yf 90-99 PAG  1-10 CO₂ 90-99 POE  1-10 2 1234yf 80-89 PAG 11-20 CO2 80-90 POE 11-20 4 1234yf 90-99 POE  1-10 CO2 90-99 POE  1-10 5 1234yf 80-89 POE 11-20 CO2 80-90 POE 11-20 6 1234ze(E) 90-99 PAG  1-10 CO2 90-99 POE  1-10 7 1234ze(E) 80-89 PAG 11-20 CO2 80-90 POE 11-20 8 1234ze(E) 90-99 POE  1-10 CO2 90-99 POE  1-10 9 1234ze(E) 80-89 POE 11-20 CO2 80-90 POE 11-20 10 SR1 90-99 PAG  1-10 CO2 90-99 POE  1-10 11 SR1 80-89 PAG 11-20 CO2 80-90 POE 11-20 12 SR1 90-99 POE  1-10 CO2 90-99 POE  1-10 13 SR1 80-89 POE 11-20 CO2 80-90 POE 11-20 14 SR2 90-99 PAG  1-10 CO2 90-99 POE  1-10 15 SR2 80-89 PAG 11-20 CO2 80-90 POE 11-20 16 SR2 90-99 POE  1-10 CO2 90-99 POE  1-10 17 SR2 80-89 POE 11-20 CO2 80-90 POE 11-20 18 SR3 90-99 PAG  1-10 CO2 90-99 POE  1-10 19 SR3 80-89 PAG 11-20 CO2 80-90 POE 11-20 20 SR3 90-99 POE  1-10 CO2 90-99 POE  1-10 21 SR3 80-89 POE 11-20 CO2 80-90 POE 11-20 22 SR4 90-99 PAG  1-10 CO2 90-99 POE  1-10 23 SR4 80-89 PAG 11-20 CO2 80-90 POE 11-20 24 SR4 90-99 POE  1-10 CO2 90-99 POE  1-10 25 SR4 80-89 POE 11-20 CO2 80-90 POE 11-20 26 SR5 90-99 PAG  1-10 CO2 90-99 POE  1-10 27 SR5 80-89 PAG 11-20 CO2 80-90 POE 11-20 28 SR5 90-99 POE  1-10 CO2 90-99 POE  1-10 29 SR5 80-89 POE 11-20 CO2 80-90 POE 11-20 30 SR6 90-99 PAG  1-10 CO2 90-99 POE  1-10 31 SR6 80-89 PAG 11-20 CO2 80-90 POE 11-20 32 SR6 90-99 POE  1-10 CO2 90-99 POE  1-10 33 SR6 80-89 POE 11-20 CO2 80-90 POE 11-20 34 SR7 90-99 PAG  1-10 CO2 90-99 POE  1-10 35 SR7 80-89 PAG 11-20 CO2 80-90 POE 11-20 36 SR7 90-99 POE  1-10 CO2 90-99 POE  1-10 37 SR7 80-89 POE 11-20 CO2 80-90 POE 11-20 38 SR8 90-99 PAG  1-10 CO2 90-99 POE  1-10 39 SR8 80-89 PAG 11-20 CO2 80-90 POE 11-20 40 SR8 90-99 POE  1-10 CO2 90-99 POE  1-10 41 SR8 80-89 POE 11-20 CO2 80-90 POE 11-20 41 SR9 90-99 PAG  1-10 CO2 90-99 POE  1-10 42 SR9 80-89 PAG 11-20 CO2 80-90 POE 11-20 43 SR9 90-99 POE  1-10 CO2 90-99 POE  1-10 44 SR10 90-99 PAG  1-10 CO2 90-99 POE  1-10 45 SR10 80-89 PAG 11-20 CO2 80-90 POE 11-20 46 SR10 90-99 POE  1-10 CO2 90-99 POE  1-10 47 SR10 80-89 POE 11-20 CO2 80-90 POE 11-20 48 SR11 90-99 PAG  1-10 CO2 90-99 POE  1-10 49 SR11 80-89 PAG 11-20 CO2 80-90 POE 11-20 50 SR11 90-99 POE  1-10 CO2 90-99 POE  1-10 51 SR11 80-89 POE 11-20 CO2 80-90 POE 11-20 52 SR12 90-99 PAG  1-10 CO2 90-99 POE  1-10 53 SR12 80-89 PAG 11-20 CO2 80-90 POE 11-20 54 SR12 90-99 POE  1-10 CO2 90-99 POE  1-10 55 SR12 80-89 POE 11-20 CO2 80-90 POE 11-20 56 SR13 90-99 PAG  1-10 CO2 90-99 POE  1-10 57 SR13 80-89 PAG 11-20 CO2 80-90 POE 11-20 58 SR13 90-99 POE  1-10 CO2 90-99 POE  1-10 59 SR13 80-89 POE 11-20 CO2 80-90 POE 11-20 60 SR14 90-99 PAG  1-10 CO2 90-99 POE  1-10 61 SR14 80-89 PAG 11-20 CO2 80-90 POE 11-20 62 SR14 90-99 POE  1-10 CO2 90-99 POE  1-10 63 SR14 80-89 POE 11-20 CO2 80-90 POE 11-20 64 SR15 90-99 PAG  1-10 CO2 90-99 POE  1-10 65 SR15 80-89 PAG 11-20 CO2 80-90 POE 11-20 66 SR15 90-99 POE  1-10 CO2 90-99 POE  1-10 67 SR15 80-89 POE 11-20 CO2 80-90 POE 11-20 68 SR16 90-99 PAG  1-10 CO2 90-99 POE  1-10 69 SR16 80-89 PAG 11-20 CO2 80-90 POE 11-20 70 SR16 90-99 POE  1-10 CO2 90-99 POE  1-10 71 SR16 80-89 POE 11-20 CO2 80-90 POE 11-20 72 SR17 90-99 PAG  1-10 CO2 90-99 POE  1-10 73 SR17 80-89 PAG 11-20 CO2 80-90 POE 11-20 74 SR17 90-99 POE  1-10 CO2 90-99 POE  1-10 75 SR17 80-89 POE 11-20 CO2 80-90 POE 11-20 76 SR18 90-99 PAG  1-10 CO2 90-99 POE  1-10 77 SR18 80-89 PAG 11-20 CO2 80-90 POE 11-20 78 SR18 90-99 POE  1-10 CO2 90-99 POE  1-10 79 SR18 80-89 POE 11-20 CO2 80-90 POE 11-20 80 SR19 90-99 PAG  1-10 CO2 90-99 POE  1-10 81 SR19 80-89 PAG 11-20 CO2 80-90 POE 11-20 82 SR19 90-99 POE  1-10 CO2 90-99 POE  1-10 83 SR19 80-89 POE 11-20 CO2 80-90 POE 11-20 84 SR20 90-99 PAG  1-10 CO2 90-99 POE  1-10 85 SR20 80-89 PAG 11-20 CO2 80-90 POE 11-20 86 SR20 90-99 POE  1-10 CO2 90-99 POE  1-10 87 SR20 80-89 POE 11-20 CO2 80-90 POE 11-20 88 SR21 90-99 PAG  1-10 CO2 90-99 POE  1-10 89 SR21 80-89 PAG 11-20 CO2 80-90 POE 11-20 90 SR21 90-99 POE  1-10 CO2 90-99 POE  1-10 91 SR21 80-89 POE 11-20 CO2 80-90 POE 11-20 92 SR22 90-99 PAG  1-10 CO2 90-99 POE  1-10 93 SR22 80-89 PAG 11-20 CO2 80-90 POE 11-20 94 SR22 90-99 POE  1-10 CO2 90-99 POE  1-10 95 SR22 80-89 POE 11-20 CO2 80-90 POE 11-20 96 SR23 90-99 PAG  1-10 CO2 90-99 POE  1-10 97 SR23 80-89 PAG 11-20 CO2 80-90 POE 11-20 98 SR23 90-99 POE  1-10 CO2 90-99 POE  1-10 99 SR23 80-89 POE 11-20 CO2 80-90 POE 11-20 100 SR24 90-99 PAG  1-10 CO2 90-99 POE  1-10 101 SR24 80-89 PAG 11-20 CO2 80-90 POE 11-20 102 SR24 90-99 POE  1-10 CO2 90-99 POE  1-10 103 SR24 80-89 POE 11-20 CO2 80-90 POE 11-20 104 SR25 90-99 PAG  1-10 CO2 90-99 POE  1-10 105 SR25 80-89 PAG 11-20 CO2 80-90 POE 11-20 106 SR25 90-99 POE  1-10 CO2 90-99 POE  1-10 107 SR25 80-89 POE 11-20 CO2 80-90 POE 11-20 108 SR26 90-99 PAG  1-10 CO2 90-99 POE  1-10 109 SR26 80-89 PAG 11-20 CO2 80-90 POE 11-20 110 SR26 90-99 POE  1-10 CO2 90-99 POE  1-10 111 SR26 80-89 POE 11-20 CO2 80-90 POE 11-20 112 SR27 90-99 PAG  1-10 CO2 90-99 POE  1-10 113 SR27 80-89 PAG 11-20 CO2 80-90 POE 11-20 114 SR27 90-99 POE  1-10 CO2 90-99 POE  1-10 115 SR27 80-89 POE 11-20 CO2 80-90 POE 11-20 116 SR28 90-99 PAG  1-10 CO2 90-99 POE  1-10 117 SR28 80-89 PAG 11-20 CO2 80-90 POE 11-20 118 SR28 90-99 POE  1-10 CO2 90-99 POE  1-10 119 SR28 80-89 POE 11-20 CO2 80-90 POE 11-20 120 SR29 90-99 PAG  1-10 CO2 90-99 POE  1-10 121 SR29 80-89 PAG 11-20 CO2 80-90 POE 11-20 122 SR29 90-99 POE  1-10 CO2 90-99 POE  1-10 123 SR29 80-89 POE 11-20 CO2 80-90 POE 11-20 124 SR30 90-99 PAG  1-10 CO2 90-99 POE  1-10 125 SR30 80-89 PAG 11-20 CO2 80-90 POE 11-20 126 SR30 90-99 POE  1-10 CO2 90-99 POE  1-10 127 SR30 80-89 POE 11-20 CO2 80-90 POE 11-20 128 SR31 90-99 PAG  1-10 CO2 90-99 POE  1-10 129 SR31 80-89 PAG 11-20 CO2 80-90 POE 11-20 130 SR31 90-99 POE  1-10 CO2 90-99 POE  1-10 131 SR31 80-89 POE 11-20 CO2 80-90 POE 11-20 132 SR32 90-99 PAG  1-10 CO2 90-99 POE  1-10 133 SR32 80-89 PAG 11-20 CO2 80-90 POE 11-20 134 SR32 90-99 POE  1-10 CO2 90-99 POE  1-10 135 SR32 80-89 POE 11-20 CO2 80-90 POE 11-20 136 SR33 90-99 PAG  1-10 CO2 90-99 POE  1-10 137 SR33 80-89 PAG 11-20 CO2 80-90 POE 11-20 138 SR33 90-99 POE  1-10 CO2 90-99 POE  1-10 139 SR33 80-89 POE 11-20 CO2 80-90 POE 11-20

System Operating Conditions

It is generally contemplated that operating conditions used in the present systems and methods can be varied widely in view of the disclosure contained herein depending upon the specific applications. However, many preferred applications will advantageously use operating parameters within the ranges indicated in the table below, with all amounts understood to be modified by “about”:

BROAD INTERMEDIATE NARROW Evaporating   −45 to −25   −40 to −30 −35 temperature of the low stage evaporator, ° C. Condensing −10 to 10 −5 to 5 0 temperature of the low-stage, ° C. Evaporating temperature −15 to 5  −10 to 0  −5 of the high-stage, ° C. Condensing 35 to 55 40 to 50 45C Temperature of the high-stage, ° C. Evaporator  0 to 15  0 to 10 5 Superheat (each stage), ° C. Temperature rise  5 to 25 10 to 20 15 in the suction line of the low-stage, ° C. Temperature rise  0 to 15  0 to 10 5 in the suction line of the high- stage, ° C. Subcooling at both  0 to 10  0 to 5 0 expansion devices of high and low stages, ° C. Compressor discharge from about 120 from about 125 not greater temperature (low and to about130 to about 130 than 125 high stage), ° C.

When operating within the process conditions according to the present invention, the use of the suction line heat exchanger as described herein preferably produces at least a 2% COP improvement, more preferably at least about 3% COP improvement, and even more preferably a 4% COP improvement compared to the same system but without a suction-line heat exchanger according to the present invention.

In the following descriptions, components or elements of the system which are or can be generally the same or similar in different embodiments are designated with the same number or symbol.

One preferred refrigeration system is illustrated in FIG. 1. The refrigeration system is designated generally as 10. The boundaries designates generally as 100 represent schematically the enclosure. The low temperature loop comprises compressor 11, condensing side 12A of the cascade exchange 12, expansion valve 14 and evaporator 15. As illustrated, evaporator 15 is located within enclosure 100, together with any of the associated conduits and other connecting and related equipment to transport the first heat transfer composition to and from the enclosure boundary. Although the evaporator 14 is preferably located inside the enclosure, and is disclosed in the illustrated figure as being located inside of the enclosure 100, it will be appreciated that in certain embodiments it may be desirable and/or necessary to provide the expander 14 outside of the enclosure. The high temperature loop comprises compressor 21, evaporating side 12B of the cascade exchange 12, expansion valve 24 and condenser 25, all located outside of enclosure 100, together with any of the associated conduits and other connecting and related equipment. The high temperature circuit also includes suction line heat exchanger 50 which enables the exchange of heat between the second heat transfer composition stream 30 exiting condenser 25 and the second heat transfer composition stream 31 exiting the evaporating side 12B of the cascade heat exchanger 12.

Although it is contemplated that the relative size of the first and second refrigeration loops according to the present invention maybe vary widely within the scope hereof, applicants have found that highly advantageous results can be achieved in certain embodiments by judicious selection of the relative sizes of the refrigeration loops. More specifically, it is contemplated and understood that under normal operating conditions the heat transfer composition contained in the first refrigeration loop and in the second refrigeration loop will never mix or intermingle. However, applicants have come to appreciate that the possibility of such intermixing of first and second refrigerants might occur for example, in the case of leakage in the cascade heat exchanger. This mixed refrigerant stream may then, in the event of a leak within the enclosure being cold, become exposed to humans or other animals located in or near the enclosure. Accordingly, in order to ensure continued safe operation even in the case of such leakage, applicants have come to appreciate that careful and judicious selection of the relative refrigeration loop sizes can result in a safe system even in the event of such a leakage.

While applicants contemplate that the systems and compositions of the present invention will be useful in many refrigeration applications, preferred applications include refrigeration systems and methods used in applications such as treating the air, including cooling and/or heating, in enclosures such as residential dwellings, office space, warehouses and the like, and in connection with enclosures used to keep items cool by cooling the air in the enclosure, such as walk-in boxes, cold-boxes, transport refrigeration boxes and the like. As used herein, the term “transport refrigeration box” is used to designate cold/insulated boxes which are located on or comprise a portion or substantially all of a truck trailer. Furthermore, in preferred applications the capacity of the system according to the present invention is less than about 30 kW. In preferred applications the capacity of the system according to the present invention is less than about 15 kW, and in yet further applications the capacity of the system according to the present invention is less than about 10 kW.

Examples of several preferred systems, methods and compositions are described below:

A. First Refrigerant is CO2 and Second Refrigerant is R-1234ze(E)

By way of example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 in the second refrigerant consists of R01234ze(E). In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

Composition Ratio Number R1234ze CO₂ CO₂ to R1234ze Flammability 1 99%  1% 0.01 Vapor and liquid flammable 2 90% 10% 0.11 Liquid flammable 3 70% 30% 0.43 Liquid flammable 4 50% 50% 1.00 Liquid flammable 5 46% 54% 1.17 Non-Flammable 6 40% 60% 1.50 Non-Flammable 7 30% 70% 2.33 Non-Flammable 8  5% 95% 19.00 Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of R-1234ze(E), it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. R-1234ze(E)) is not less than about 1.2. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

B. First Refrigerant is CO2 and Second Refrigerant is SR26

By way of further example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of a SR26 (80:20 weight ratio combination of R-1234ze(E);R-32). In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

Composition Ratio R1234ze + R32 CO₂ to Number (0.8/0.2) CO₂ R1234ze + R32 Flammability 1 100%   0% 0 Vapor and liquid flammable 2 99%  1% 0.01 Vapor and liquid flammable 3 90% 10% 0.11 Liquid flammable 5 70% 30% 0.43 Liquid flammable 6 50% 50% 1.00 Liquid flammable 7 49% 51% 1.04 Non-Flammable 8 40% 60% 1.50 Non-Flammable 9 30% 70% 2.33 Non-Flammable 10  5% 95% 19.00 Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 1.0. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

C. First Refrigerant is CO2 and Second Refrigerant is R-32

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of a R-32. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

Composition Ratio Number R32 CO₂ CO₂ to R32 Flammability 1 100%   0% 0 Vapor and liquid flammable 2 99%  1% 0.01 Vapor and liquid flammable 3 90% 10% 0.11 Vapor and liquid flammable 4 80% 20% 0.25 Liquid flammable 5 70% 30% 0.43 Liquid flammable 6 60% 40% 0.67 Liquid flammable 7 53% 47% 0.89 Non-Flammable 8 50% 50% 1.00 Non-Flammable 9 40% 60% 1.50 Non-Flammable 10 10% 90% 9.00 Non-Flammable 11  5% 95% 19.00 Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 0.9. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

D. First Refrigerant is CO2 and Second Refrigerant is Ethane

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of ethane. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

Composition Ratio Number Ethane CO₂ CO₂ to Ethane Flammability 1 100%  0% 0 Vapor and liquid flammable 2  90% 10% 0.11 Vapor and liquid flammable 3  80% 20% 0.25 Vapor and liquid flammable 4  70% 30% 0.43 Liquid flammable 5  60% 40% 0.67 Liquid flammable 6  50% 50% 1.00 Liquid flammable 7  40% 60% 1.50 Liquid flammable 8  37% 63% 1.70 Non-Flammable 9  30% 70% 2.33 Non-Flammable 10  20% 80% 4.00 Non-Flammable 11  10% 90% 9.00 Non-Flammable 12  5% 95% 19.00 Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of ethane, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 1.7. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

E. First Refrigerant is CO2 and Second Refrigerant is Propane

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of propone. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

Composition Ratio Number Propane CO₂ CO₂ to Propane Flammability 1 100%  0% 0 Vapor and liquid flammable 2  90% 10% 0.11 Liquid flammable 3  80% 20% 0.25 Liquid flammable 4  70% 30% 0.43 Liquid flammable 5  60% 40% 0.67 Liquid flammable 6  50% 50% 1.00 Liquid flammable 7  40% 60% 1.50 Liquid flammable 8  30% 70% 1.70 Liquid flammable 9  20% 80% 1.50 Liquid flammable 10  10% 90% 9.00 Non-Flammable 11  5% 95% 19.00 Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of propane, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. propane) is greater than 4. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

EXAMPLES Comparative Example C1

Comparative Example Cl as described below is based on a typical walk-in cooler refrigeration system as illustrated in FIG. 2.

In FIG. 2, the boundaries of the cooler are represented schematically by the box 100. Enclosed within the cooler box is the evaporator 15 and expander 14. Compressor 11 and condenser 20 are located outside the cooler box 100. The refrigerant circulating within this refrigeration loop is refrigerant R-404A (52 wt. % R-143a, 44 wt. % R-125 and 4 wt. % R-134a).

The following operating parameters are used:

-   -   Evaporating temperature of evaporator 15=−35° C.     -   Condensing temperature of condenser 200=45° C.     -   Isentropic efficiency of expander 14=63%     -   Evaporator Superheat=5° C.     -   Temperature rise in the compressor suction line=20° C.     -   Expansion device subcooling=0° C.         The operation of this typical system produces a compressor         discharge temperature of 108.3° C.

Hybrid Examples H1A-H1D

A hybrid system based on the typical refrigeration system as illustrated in Example 1 is formed but a suction line heat exchanger is inserted so as to absorb heat into the R-404A exiting the evaporator and thereby increasing the temperature of R-404A entering the compressor by absorbing heat from R-404A exiting the condenser prior to that stream entering expander. Operation using a suction line heat exchanger with Effectiveness values varying from 35% to 85% are evaluated. The results are reported in the following Table H1, together with the result of comparative Example C1 for comparison:

TABLE H1 C1 H1A H1B H1C H1D Effectiveness,  0 (no heat 35 55 75 85 %* exchanger) Compressor 108.3 133.1 150.0 166.5 174.7 Discharge Temperature, ° C. *Effectiveness % of the suction line heat exchanger as used herein refers to the percentage of ideal operation with no heat loss

As can be seen from the results reported above, modifying a typical system to include a suction line heat exchanger is not viable since in every case there is a substantial, and unwanted and undesirable, increase in the compressor discharge temperature as a result of operating such a hybrid system.

Examples 1A-1E, 2A-2E, 3A-3E, 4A-4E and 5A-5E

A cascade refrigeration system having a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant): HFO-1234ze(E); HFO-1234yf; SR21(80 wt % HFO-1234yf and 20 wt % R-32); SR26 (80 wt % HFO-1234ze(E) and 20 wt % R-32); and SR31(88 wt % HFO-1234ze(E) and 12 wt % R-32). The refrigerant in the high temperature loop is CO₂. Using these refrigerants, the cascade system of the present invention is operated according to the following parameters:

-   -   Evaporating temperature of the low stage (evaporator 15)=−35° C.     -   Condensing temperature of the low-stage=(cascade condenser         12A)=0° C.     -   Evaporating temperature of the high-stage (evaporator 25)=−5° C.     -   Condensing Temperature of the high-stage (cascade condenser         12B)=45° C.     -   Isentropic efficiency of the low-stage expander (expander         14)=65%     -   Isentropic efficiency of the high-stage expander (expander         24)=63%     -   Evaporator Superheat (both evaporators)=5° C.     -   Temperature rise in the suction line of the low-stage=15° C.     -   Temperature rise in the suction line of the high-stage=5° C.     -   Subcooling at both expansion devices of high and low stages=0°         C.     -   Suction-line Liquid-line heat exchanger Effectiveness=vary from         0% to 85%.         Table 1/5-DT below shows the results in terms of discharge         temperature for each example, with result from Comparative         Example 1 being shown for comparison:

TABLE 1/5 DT C1 and 1A-5A 1B-5B 1C-5C 1D-5D 1E-5E Effective-  0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant Compressor Discharge Temperature, ° C. R-404A 108.3 133.1 150.0 166.5 174.7 HFO-  70 87 97 106 111 1234ze(E) (Examples 1A-1E) HFO-1234yf  65 81 91 100 105 (Examples 2A-2E) SR21  68 85 95 104 109 (Examples 3A-3E) SR26  88 102 110 117 121 (Examples 4A-4E) SR31  81 96 104 112 116 (Examples 5A-5E)

As revealed by the table above, all Examples of the present invention satisfy the preferred compressor discharge temperatures of the present invention, and in all cases the discharge temperature is substantially superior to the performance of the typical system and even the hybrid system.

Table 1/5-COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 1/5 COP C1 and 1A-5A 1B-5B 1C-5C 1D-5D 1E-5E Effective- 0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant COP (COP/% COP compared to Comparative Example 1) R-404A 0.89/100 HFO- 1.12/125 1.14/128 1.16/130 1.17/131 1.18/132 1234ze(E) (Examples 1A-1E) HFO-1234yf 1.07/121 1.11/125 1.13/127 1.15/129 1.16/130 (Examples 2A-2E) SR21 1.11/125 1.39/128 1.15/130 1.17/131 1.18/132 (Examples 3A-3E) SR26 1.11/125 1.13/127 1.14/128 1.15/129 1.16/130 (Examples 4A-4E) SR31 1.08/121  1.1/123 1.11/125 1.12/126 1.13/127 (Examples 5A-5E)

As revealed by the table above, all Examples of the present invention result in improved COP of at least 121% compared to the system of Comparative Example 1. In addition all systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without heat exchanger, and a systems with 55% or higher heat exchanger effectiveness for the suction line heat exchanger show at least an additional 3% improvement versus the system without heat exchanger.

Examples 6A-6E, 7A-7E, 8A-8E, 9A-9E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO₂ in the high temperature loop (showing the GWP of each refrigerant):

Component>>> Second Refrigerant Designation R-1234ze(E), ▾ ▾ wt % R-32, wt % GWP EX6 0 100 677 EX7 10 90 609 EX8 20 80 542 EX9 30 70 474

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX6-EX9, and Table 6/9-DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 6/9 DT C1 and 6A-9A 6B-9B 6C-9C 6D-9D 6E-9E Effective-  0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant Compressor Discharge Temperature, ° C. R-404A 108 133 150 167.5 175 Examples 125 145 157 168 174 6A-6E) Examples 121 140 151 162 167 7A-7E) Examples 117 136 146 156 161 7A-7E Examples 113 130 140 150 154 7A-7E

As revealed by the table above, using the refrigerants EX6-EX9 produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems without a suction line heat exchanger (effectiveness=0). However, none of the refrigerants produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems for any of the values of effectiveness from 35% to 85%.

Examples 10A -10E, 11A -11E, 12A-12E, 13A-13E, 14A-14E, 15A-15E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO2 in the high temperature loop:

Component>>> Second Refrigerant Designation R-1234ze(E), ▾ ▾ wt % R-32, wt % GWP EX10 40 60 407 EX11 50 50 339 EX12 60 40 271 EX13 70 30 204 EX14 80 20 136 EX15 90 10 69

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX10-EX15, and Table 10/15-DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 10/15 DT C1 and 10A-15 10B-15B 10C-15C 10D-15D 10E-15E Effective-  0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant Compressor Discharge Temperature, ° C. R-404A 108 133 150 167.5 175 Examples 109 125 134 143 148 10A-10E Examples 104 120 128 137 141 11-11E Examples 100 114 122 130 134 12A-12E Examples  94 108 116 124 128 13A-13E Examples  88 102 110 117 121 14A-14E Examples  81 95 103 111 115 15A-15E

As revealed by the table above, using the refrigerants EX10-EX15 results in a second refrigerant with a GWP value below 500, but not each refrigerant produces an acceptable discharge temperature (i.e., within the scope of preferred discharge temperature range). For cascade systems without a suction line heat exchanger (effectiveness=0), the discharge temperature is acceptable. However, for systems with a suction line heat exchanger, each of EX10 -EX13 refrigerants produce unacceptable discharge temperatures for the desired effectiveness values of 85% or above. Only EX 14 and EX 15 provide acceptable discharge temperatures for suction line heat exchangers having any of the tested effectiveness values. These finding are summarized below:

-   -   At 35% effectiveness, greater than 30% of R1234ze(E) is required     -   At 55% effectiveness: greater than 50% of R1234ze(E) is required     -   At 75% effectiveness: greater than 60% of R1234ze(E) is required     -   At 85% effectiveness: greater than 70% of R1234ze(E) is required     -   Compositions containing at least about 78% of R-1234ze(E) are         acceptable for all effectiveness values of the suction line heat         exchanger and produce a GWP value of about 150 or less.

Table 11/15-COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 10/15 COP C1 and 10A-15A 10B-15B 10C-15C 10D-15D 10E-15E Effective- 0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant COP (COP/% COP compared to Comparative Example 1) R-404A 0.89/100 Examples  1.1/123 1.11/124 1.1/124 1.1/124 1.1/124 10A-10E Examples  1.1/124  1.1/124 1.1/125 1.1/125 1.1/125 11-11E Examples  1.1/124  1.1/125 1.1/125 1.1/126 1.1/126 12A-12E Examples  1.1/125  1.1/127 1.1/128 1.2/129 1.2/130 13A-13E Examples  1.1/125  1.1/127 1.1/129 1.2/130 1.2/131 14A-14E Examples  1.1/125  1.1/128 1.2/130 1.2/131 1.2/132 15A-15E

As revealed by the table above, all Examples of the present invention result a COP of at least 121% compared to the system of Comparative Example 1. In addition the use of the refrigerant of Example 15 in all tested systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, The use of the refrigerant of Example 14 in tested systems of the present invention which include a suction-line heat exchanger with and effectiveness of at least 55% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger and (as shown in Table 11/15-DT) have an acceptable discharge temperature. The use of the refrigerant of Example 13 in tested systems of the present invention which include a suction-line heat exchanger with and effectiveness of at least 55% but less than about 85% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger and (as shown in Table 11/15-DT) have an acceptable discharge temperature.

In contrast, while the use of the refrigerant of Example 12 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of at least 75% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, as shown in Table 11/15-DT, this refrigerant does not provide an acceptable discharge temperature for this conditions.

Examples 16A-16E, 17A-17E, 18A-18E, 19A-19E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the high temperature loop (the second refrigerant) and CO₂ in the low temperature loop (showing the GWP of each refrigerant):

Component>>> Second Refrigerant Designation R-1234yf, ▾ ▾ wt % R-32, wt % GWP EX16 0 100 677 EX17 10 90 609 EX18 20 80 542 EX19 30 70 474

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX16-EX19, and Table 16/19-DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 16/19 DT C1 and 16A-19A 16B-19B 16C-19C 16D-19D 16E-19E Effective-  0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant Compressor Discharge Temperature, ° C. R-404A 108 133 150 167.5 175 Examples 125 145 157 168 174 16A-16E) Examples 119 138 149 160 166 17A-17E) Examples 113 132 142 153 158 18A-18E Examples 107 125 136 146 151 19A-19E

As revealed by the table above, using the refrigerants EX16-EX19 produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems without a suction line heat exchanger (effectiveness=0). However, none of the refrigerants produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems for any of the values of effectiveness from 35% to 85%.

Examples 20A-20E, 21A-21E, 22A-22E, 23A-23E, 24A-24E, 25A-25E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO2 in the high temperature loop:

Component>>> Second Refrigerant Designation R-1234ze(E), ▾ ▾ wt % R-32, wt % GWP EX20 40 60 407 EX21 50 50 339 EX22 60 40 271 EX23 70 30 204 EX24 80 20 136 EX25 90 10 69

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX20-EX25, and Tables 20/25-DT below shows the results in terms of discharge temperature for each example, with result from Comparative

Example 1 being shown for comparison:

TABLE 20/25 DT C1 and 20A-25 20B-25B 20C-25C 20D-25D 20E-25E Effective-  0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant Compressor Discharge Temperature, ° C. R-404A 108 133 150 167.5 175 Examples 102 125 134 143 148 20A-20E Examples  97 113 123 132 137 21-21E Examples  92 107 116 125 130 22A-22E Examples  86 102 110 119 123 23A-23E Examples  81 96 109 112 116 24A-24E Examples  74 89 97 105 110 25A-25E

As revealed by the table above, using the refrigerants EX21-EX25 results in a second refrigerant with a GWP value below 500, but not each refrigerant produces an acceptable discharge temperature (i.e., within the scope of preferred discharge temperature range). For cascade systems without a suction line heat exchanger (effectiveness=0), the discharge temperature is acceptable. However, for systems with a suction line heat exchanger, each of refrigerants EX20-EX22 produces unacceptable discharge temperatures for the desired effectiveness values of 85% or above. Only EX 23, EX24 and EX 25 provide acceptable discharge temperatures for suction line heat exchangers for all tested effectiveness values. These findings are summarized below:

-   -   At 35% effectiveness, greater than 30% of R1234yf is required     -   At 55% effectiveness: greater than 40% of R1234yf is required     -   At 75% and 85% effectiveness: greater than 60% of R1234yf is         required

Table 20/25-COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 20/25 COP C1 and 20A-25A 20B-25B 20C-25C 20D-25D 20E-25E Effective- 0 (no heat 35 55 75 85 ness, %* exchanger) Refrigerant COP (COP/% COP compared to Comparative Example 1) R-404A 0.89/100 Examples  1.1/122 1.11/122 1.1/122 1.1/122 1.1/122 20A-20E Examples  1.1/121  1.1/122 1.1/123 1.1/123 1.1/123 21-21E Examples  1.1/121  1.1/122 1.1/123 1.1/124 1.1/124 22A-22E Examples  1.1/121  1.1/123 1.1/124 1.2/125 1.2/125 23A-23E Examples  1.1/121  1.1/123 1.1/124 1.1/126 1.1/127 24A-24E Examples  1.1/121  1.1/124 1.1/126 1.1/128 1.2/129 25A-25E

As revealed by the table above, all Examples of the present invention result a COP of at least 121% compared to the system of Comparative Example 1. In addition the use of the refrigerant of Examples 24 and 25 in all tested systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, and the refrigerant of Examples 22 and 23 shows at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger for heat exchangers with effectiveness of 55% or greater. The use of the refrigerant of Examples 22 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of at least 75% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger.

Importantly, the use of the refrigerant of Examples 24 and 25 in all tested systems of the present invention which include a suction-line heat exchanger not only show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, such refrigerants (as shown in Table 21/25-DT) have an acceptable discharge temperature for all levels of suction line heat exchanger effectiveness tested. The use of the refrigerant of Examples 22 and 23 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of 55% show not only at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger but (as shown in Table 21/25-DT) also have an acceptable discharge temperature.

In contrast, while the use of the refrigerant of Example 20 does not demonstrate at least a 2% improvement for any values of heat exchanger effectiveness, and while Examples 21 and 22 show at least a 2% improvement for heat exchanger effectiveness values of 75% and 85%, these values of heat exchanger effectively do not does not provide an acceptable discharge, as shown in Table 20/25-DT, this refrigerant does not for this conditions. 

What is claimed is:
 1. A heat transfer system for cooling the contents of an enclosure comprising: (a) a relatively low temperature vapor compression loop comprising a compressor, an expander and an evaporator in fluid communication in said loop, and a first heat transfer composition in said loop comprising a first refrigerant and lubricant for the compressor, said evaporator being located in said enclosure and being capable of absorbing heat from fluid in said enclosure at about said relatively low temperature; (b) a relatively high temperature vapor compression loop comprising a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication in said loop, and a second heat transfer composition in said loop comprising a second refrigerant and preferably lubricant for the compressor, said condenser being capable of transferring heat to a heat sink located outside said enclosure; and (c) a cascade heat exchanger for condensing said first refrigerant and evaporating said second refrigerant by heat exchange between said first and second refrigerant, wherein said suction line heat exchanger is in fluid communication with said cascade heat exchanger for receiving at least a portion of said second heat transfer composition exiting said cascade heat exchanger and increases the temperature thereof by absorbing heat from said first heat transfer composition exiting said condenser and thereby reducing the temperature of said first heat transfer composition prior to said first heat transfer composition entering said first loop expander.
 2. The system of claim 1 wherein the first refrigerant has a flammability that is substantially less than the flammability of the second refrigerant.
 3. The system of claim 1 wherein the first refrigerant has a flammability classified as Al under ASHRAE 34 (as measured by ASTM E681) and the second refrigerant has a flammability that is classified as A2L under ASHRAE 34 (as measured by ASTM E681) or a higher flammability than A2L.
 4. The system of claim 1 wherein the first and the second refrigerant each have a Global Warming Potential (GWP) that is less than about
 150. 5. The system of claim 1 wherein each of said compressors and said expanders and said condenser are not located in the enclosure.
 6. The system of claim 5 wherein the suction line heat exchanger is not located in the enclosure.
 7. The system of claim 1 wherein said second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, R-32 and combinations of two or more of these.
 8. The system of claim 1 wherein said second refrigerant comprises at least about 80% by weight of 2, 3,3,3-tetrafluoropropene (HFO-1234yf).
 9. The system of claim 1 wherein said second refrigerant consists essentially of HFO-1234ze(E), HFO-1234yf or combinations of these.
 10. The system of claim 1 wherein said second refrigerant comprises from about 70% by weight to about 90% by weight of HFO-1234yf and from about 10% by weight to about 30% by weight of R32.
 11. The system of claim 10 wherein said second refrigerant comprises from about 80% by weight of HFO-1234yf and about 20% by weight of R32.
 12. The system of claim 1 wherein said second refrigerant comprises from about 70% by weight to about 90% by weight of HFO-1234yze(E) and from about 10% by weight to about 30% by weight of R32.
 13. The system of claim 1 wherein said second refrigerant comprises about 80% by weight of HFO-1234ze(E) and about 20% by weight of R32.
 14. The system of claim 1 wherein said second refrigerant comprises from about 85% to about 90% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight to about 15% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).
 15. The system of claim 1 wherein said second refrigerant comprises from about 88% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight to about 12% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).
 16. The system of claim 1 wherein the evaporating temperature of said first refrigerant in said relatively low temperature vapor compression loop is from about −45° C. to about −25° C.
 17. The system of claim 16 wherein the evaporating temperature of said second refrigerant in said relatively high temperature vapor compression loop is from about −15° C. to about 5° C.
 18. The system of claim 17 wherein the condensing temperature of said first refrigerant in said relatively low temperature vapor compression loop is from about −5° C. to about −5° C.
 19. The system of claim 18 wherein the condensing temperature of said second refrigerant in said relatively high temperature vapor compression loop is from about 40° C. to about 50° C.
 20. The system of claim 19 wherein said first refrigerant comprises carbon dioxide and said second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, R-32 and combinations of two or more of these. 